Products in Focus | Power Supplies
Author details:
Ying Cheng and Zhongming
Ye are both senior
applications engineers at
Analog Devices
20A current capability, multiple
LTC7150Ss can be paralleled and run
out-of-phase.
The LTC7150S features a sync
function that enables synchronisation
to an external clock, and the internal
PLL (phase-locked loop) allows the
LTC7150S to be operated out-ofphase
for multichannel, multiphase
operation to reduce ripple.
The CLKOUT signal can be
connected to the MODE/SYNC pin
of a following LTC7150S to line up
both the frequency and the phase
of the entire system. Multiphase
operation is implemented at the
PHMODE pin.
Tying the PHMODE pin to
INTVCC, SGND, or floating the pin
generates a phase difference between
the clock applied on the MODE/
SYNC pin and CLKOUT; differences
of 180°, 120°, or 90°, respectively,
corresponding to 2-phase, 3-phase,
or 4-phase operation. A total of 12
channels can be run out-of-phase with
respect to each other by programming
the PHMODE pin of each LTC7150S
to different voltage levels.
Figure 1 (previous page) shows
two converters connected in parallel
to provide 40A output current at
1.2V. The clock from the master unit
is synced to the slave unit by tying
the CLKOUT of U1 to the MODE/
SYNC of U2.
The master PHMODE pin is tied
to ground, and the slave PHMODE
pin is left floating. This results in 180°
phase difference between the two
channels, reducing the input current
ripple.
To ensure better current sharing in
steady state and during startup, ITH,
FB, and TRACK/SS are tied together.
Local RT resistors are needed and
should not be tied together. Kelvin
connection is recommended for
accurate feedback and noise immunity.
Place as many power vias as possible in
the vicinity of the ground pins to the
bottom layer to improve the thermal
performance. Ceramic caps of the
input hot loops should be placed close
to the VIN pins.
The inductor current is balanced
during startup and steady state as
shown in Figure 2. Efficiency can be as
high as 89% at 32 A, when the input
is 3.3 V.
The LT8642S also features enable
control, a power good indicator, and
soft-start. These functions are essential
to the system power sequencing,
required by SoC and FPGA power
supplies.
ADI’s Power by Linear portfolio
offers a range of buck regulators to
fulfill the wide-ranging power budgets
of advanced SoCs, FPGAs, and
microprocessors.
Conclusion
The demand for more intelligence,
automation, and sensing has resulted
in a proliferation of electronic
systems that require increasingly
high-performance power supplies.
Low EMI has risen from afterthought
to top priority, while solution size,
high efficiency, thermal proficiency,
robustness, and ease-of-use remain
important.
ADI monolithic regulators look to
satisfy the requirements of automotive,
telecom, data centre and industry
customers. In particular, the family
of high-performance monolithic
regulators that includes the LTC7150S
and LT8642S meets stringent EMI
standards in a compact size by
incorporating proprietary Silent
Switcher technology.
Integrated MOSFETs and
integrated thermal management
features enable robust and reliable
delivery of current from several
amperes to beyond 20A from input
ranges up to 20V and with control,
power good indicator, and soft-start
features are included, only a few
components are needed to complete
the power supply design.
8 www.newelectronics.co.uk
www.digikey.co.uk
Figure 2:
Inductor current
waveforms for
the parallel
solution
/www.newelectronics.co.uk
/www.digikey.co.uk